1. Field of the Invention
The present invention relates to a process for the preparation of cyclopropyl alkyl ketones containing C.sub.1 - to C.sub.4 -alkyl groups from 3-acyltetrahydrofuran-2-ones.
2. Description of the Background
Cyclopropyl ketones are important intermediates for the preparation of pharmaceuticals and agrochemicals.
They are prepared by a reaction as shown in the following equation: ##STR1## 4,5-Dihydro-2-alkylfurans and carbon dioxide are byproducts of the reaction.
Processes for the preparation of cyclopropyl alkyl ketones are known as disclosed in EP-A-O 552 586 and EP-A-O 725 066. These processes involve reacting 3-acyltetrahydrofuran-2-one with alkali metal halide at a temperature from 160-220.degree. C., and then distilling and condensing cyclopropyl alkyl ketone and the byproduct 4,5-dihydro-2-alkylfuran.
In the preparation of cyclopropyl methyl ketone (CPMK) from 3-acetyltetrahydrofuran-2-one and acetylbutyrolactone (ABL), 4,5-dihydro-2-methylfuran (DHMF) is produced in amounts of, in most cases, from 5-30%, based on the total amount of CPMK and DHMF. In order to obtain high-purity CPMK, the mixture of CPMK and DHMF must be fractionated. German patent Application No. P 197 10 879.2 thus describes a continuous process for the removal of DHMF by distillation. This process, however, requires a rectification column which has a high separation efficiency.
In addition, DHMF is a compound which, according to Houben-Weyl, Methoden der Organischen Chemie, Volume Vl/3, 1965, p. 698, can react vigorously with nucleophiles in the presence of traces of acid with the release of large amounts of heat. In the preparation of CPMK on a commercial scale, the handling of such a reactive byproduct as DHMF is thus undesirable. This is because improper handling of DHMF or of a DHMF-containing fraction may be injurious for humans and the environment. A need, therefore, continues to exist for an improved method of producing CPMK which effectively separates DHMF while avoiding risk of contact with DHMF.